Is a neighborhood park in Brooklyn worth a half-billion dollars? That may be the ultimate cost of Bushwick Inlet Park, which you’ve probably never heard of. This time of year, it’s full of children from around the city playing soccer. But it’s not much to look at.

Abutting the waterfront in Williamsburg, it consists of a five-acre playing field on what used to be a lot for rental trucks in the shadow of a big, ugly CitiStorage warehouse.

The warehouse and a defunct oil fuel depot next door were to have been bought, knocked down and turned into parkland, 28 acres in all. In 2005, the Bloomberg administration promised the entire park to the neighborhood in exchange for massive, high-end rezoning in Williamsburg and Greenpoint. At that time, city officials imagined a price tag of around $60 million to $90 million.

But through a combination of factors, the city has spent some $225 million — and still has not acquired all the property. That figure already surpasses the High Line’s cost to taxpayers, and the whole park threatens to approach the amount paid for Hudson River Park, which covers 550 acres and is four miles long.

Now the de Blasio administration faces an unenviable dilemma: break the agreement the Bloomberg administration made or pay through the nose while money is needed for more affordable housing, safer streets, improved schools and libraries — and other parks.

What happened here? Bushwick Inlet is a textbook study in civic entropy and how public developments go awry, with little that neighborhoods and government can do about it. There’s no easy solution. Just hard choices.

Unsurprisingly, the first turn toward the absurd involved a lawsuit. Through eminent domain, the city offered $12 million for the rental truck lot. When the owner found a sympathetic judge, the price leapt into the stratosphere, to more than $90 million. The owner of CitiStorage, next door, Norman Brodsky, naturally assumed he had also hit the jackpot. Crain’s reported recently that he now wants $500 million for his 11-acre site. If the city won’t pony up, his site will cleave the prospective park in two.

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The Bushwick Inlet Park is someday supposed to extend to a CitiStorage warehouse and a defunct oil fuel depot, becoming 28 acres in all.CreditChristian Hansen for The New York Times

Back here on planet Earth, the city will not, and should never, pay that kind of ransom. The good news is that the site is zoned for industrial use, meaning it’s unlikely that Mr. Brodsky will find a private buyer who logically crunches the numbers and offers half the asking price. But whatever the property finally costs, it won’t include the millions needed to decontaminate that land and also the fuel oil depot, which the city is still trying to acquire for a little less than $69 million, a bargain in retrospect.

Let’s put aside how eminent domain proceedings ended up provoking a settlement that cost taxpayers more than $90 million for a truck rental lot on a decrepit industrial site. The bottom line is that the system is capricious, promotes extortion and often acts against the public interest. While private developers quietly accrue properties to assemble big projects, keeping their intentions secret and upfront costs down, government must act openly, as it should, the upshot often being that landlords can have City Hall over a barrel.

The rezoning process invariably opens the door to speculators, like the ones now in East New York, where for months the de Blasio administration has been publicly mulling over a plan to encourage subsidized housing. Speculators have been buying properties there, escalating housing prices, creating instability for poor tenants in the neighborhood before a single new subsidized apartment is built — exactly the opposite outcome intended by the prospective rezoning.

The mayor’s latest budget strengthens legal services for endangered residents in districts slated for rezoning and puts aside $1 billion as a kind of rainy-day slush fund for unanticipated costs associated with those rezonings, the example of Bushwick Inlet Park being a prime cautionary tale. Both good moves.

But last week Mayor Bill de Blasio’s parks commissioner, Mitchell J. Silver, told the City Council that there was no money in the budget to acquire CitiStorage for Bushwick Inlet, which, despite its name, lies at the heart of Williamsburg hipsterdom, in the midst of Brooklyn Bowl, the Music Hall, Brooklyn Flea and Smorgasburg. East River State Park is next door. McCarren Park is a few blocks away: The city has also poured millions into fixing it up.

Spending millions more on a park in this affluent neighborhood is not the mayor’s priority, even though he voted for the rezoning in 2005. The mayor has said he wants to fix a few dozen neglected community parks in underserved areas of New York. At the same time, he wants to cut parks funding drastically from what it was under Michael R. Bloomberg — a big disappointment and a missed opportunity to spread social equity and environmental justice.

Meanwhile, that sympathetic judge, Abraham Gerges, a former city councilman for Williamsburg, no longer sits on the bench.

So here’s one scenario: The city could test its luck again in court over CitiStorage.

Eventually, Mr. Brodsky may come to his senses and negotiate for his site with the city, or find some buyer who will need to approach City Hall with a proposal. The mayor might then try to grab a chunk of the site to meet his affordable housing commitment. His argument would be that rezoning the site for some mixed-use development would throw off money to defray park costs.

But what kind of development? How big? And how would the neighborhood be compensated? Stephen Levin, the councilman for the district, told me last week that he would vote against any rezoning. “More and more people in the community have come together around this issue,” he said.

“We have a robust capital budget in the city now, and that $1 billion is being budgeted for other areas this administration wants to rezone,” he added. “In my personal life, I try not to take on new debts before I pay off my old ones. Our community has been waiting years.” He asked how City Hall can again be relied on to fulfill its commitments if it reneges on this one.

I wondered whether there were other nearby sites to which development rights for the CitiStorage property could be transferred. Mr. Levin said there are none that wouldn’t cost the public a fortune. I mentioned a large city-owned waterfront plot near the Brooklyn Navy Yard, south of Division Avenue, which could be turned into a new park. Might that sweeten some deal, extending an already evolving network of green space along the Williamsburg waterfront?

It’s too far away from Bushwick Inlet, Mr. Levin said.

He added, “We only have one opportunity to get this right, and I’d rather wait than get it wrong.”

In its rush to rezone, the Bloomberg administration clearly failed to anticipate events.

So at this point maybe patience is the only answer. Adrian Benepe, a former city parks commissioner, reminded me of the Chelsea Recreation Center.

In 1964, Mayor John V. Lindsay’s administration decided to tear down an ancient public bathhouse on West 28th Street to make way for a mail-sorting facility, with the promise that a recreation center would be built. Construction was delayed until the mid-70s, when the fiscal crisis hit and the project halted. A quarter-century more passed. Chelsea transformed.

Then Mayor Rudolph W. Giuliani picked up the gauntlet and Mr. Bloomberg cut the ribbon in 2004. Born in an era that envisioned a home economics room for girls, the new recreation center opened in an age of stair-climbing machines.

Forty years is a very long time. But Bushwick Inlet could be a great park someday.

A version of this article appears in print on , on Page C1 of the New York edition with the headline: Price of a New Park: $225 Million and Rising . Order Reprints | Today’s Paper | Subscribe